1. Field of the Invention
The present invention relates to photosensitive resin compositions, and more specifically to negative photoresist compositions which are used for the production of semiconductors such as an integrated circuit (IC) and a large-scale integration (LSI), and a liquid crystal display (LCD).
2. Related Art
As a photoresist for producing semiconductor devices such as ICs and LSIs, at the beginning, a cyclized rubber photoresist obtained by dissolving a cyclized rubber and a photosensitive bisazide in an organic solvent was used. Irradiation with light to the cyclized rubber photoresist generates nitrene which brings about the cleavage of double bonds in the cyclized rubber to cause polymerization, thereby producing a crosslinked network polymer. With the improvement in the integration of integrated circuits, a line & space width in a resist pattern which is formed by a photoresist has been made narrower year after year. (The term "line & space width" herein is intended to refer to the width of two lines of those formed in a resist pattern at regular intervals. A resist which can reproduce patterns with a narrower line & space width is a resist capable of forming finer patterns.) Under such circumstances, the above-described cyclized rubber photoresist cannot meet the present demand for finer resist patterns any more because the rubber swells in a solution.
A positive resist prepared by the combination use of a novolak resin which does not swell in a solution at all and a naphthoquinone diazide has then been used. Furthermore, not only the materials for photoresists but light to be used for exposure has been studied in order to obtain finer patterns, and, as a result, light having a wavelength of 365 nm, called i-line, has been substituted for light having a wavelength of 436 nm, called g-line. Those photosensitive naphthoquinone diazides which can effectively act in light having such a wavelength have also been studied and selected.
However, even when the use of such a positive resist consisting of the novolak resin and the naphthoquinone azide and exposure to i-line are adopted in combination, the line & space width of a mass-produced pattern is limited to 0.5 .mu.m, that is, a so-called submicron level is the limit on a mass production scale.
In order to obtain resolution below submicron, a phase-shifting method in which a layer called a shifter is partially provided on a photomask and a phase is shifted to obtain improved resolution is now being studied. A conventional i-line exposure apparatus can be employed in this method as it is. However, a negative photoresist is suitable as a photoresist for this method, so that the development of negative photoresists is highly expected.
LCDs are also produced by using a photoresist in the same manner as in the production of semiconductors. When a positive photoresist is used as the photoresist in the production of LCDs, the resist remains at the periphery of a panel. This is not very favorable because the resist remaining at the periphery tends to fall off during the production of the panel, resulting in decrease in the production yield of the panel. For this reason, a negative photoresist which does not remain at the periphery of a panel during the production thereof is desirable for the production of LCDs. The development of suitable negative photoresists is therefore expected.
Some negative photoresists applicable to the above-described phase-shifting method for producing semiconductors or to the production of LCDs have been proposed. However, these photoresists have shortcomings in that they require a developing process using an organic solvent, and that an extremely long exposure time is required since their photosensitivity is too low. Furthermore, it is desirable that the profile of the developed photoresist be rectangular. It is, however, difficult to obtain an ideal rectangular profile by using the conventional photoresists. In some cases, whisker-like raised portions are formed in those areas from which the resist should be removed completely.